Today, most of the laser devices which emit at a wavelength band of 980 nm are made of a GaAs-based compound semiconductor material. The following describes a typical example A of such laser devices referring to FIG. 1.
This laser device A is of a ridge optical waveguide having a Fabry-Perot cavity structure. The laser device A has the following layer structure.
A lower cladding layer 2 of, for example, n-Al0 3Ga0.7As is laminated on a substrate 1 of n-GaAs, followed by a lower SCH layer 3a of, for example, non-doped Al0 2Ga0.8As.
A barrier layer 4a of non-doped GaAs0 9P0 1 and a well layer 4b of non-doped InGaAs, to be discussed later, are alternately laminated on the lower SCH layer 3a, thereby forming an active layer 4 which has a quantum well structure having two wells.
An upper SCH layer 3b of, for example, Al0.2Ga0 8As is laminated on the barrier layer 4a, the topmost layer of the active layer 4. An upper cladding layer 5 of, for example, p-Al0 3Ga0 7As and a cap layer 6 of, for example, p+-GaAs are laminated in that order on the SCH layer 3b. 
The top surface of the layer structure, excluding the top surface of the cap layer 6, is coated with a protective film 7 of, for example, silicon nitride (SiN). A p-type electrode 8 is formed in ohmic contact with the top surface of the cap layer 6 and an n-type electrode 9 is formed at the back of the substrate 1.
In this laser device A, the well layer 4b generally contains InGaAs whose InAs mole fraction is 0.15 to 0.2, and is so formed to have a distortion amount (compressive strain) of approximately 1% to 1.4%, to realize high-power lasers emitting at a wavelength band of 980 nm.
These devices have been shown to perform reliably for tens of thousands of hours at relatively high output powers of 200 mW and above before the devices degrade or undergo catastrophic optical failure (ie., irreversible failure). Nonetheless, there is a growing demand for laser devices which can operate at these power levels and above for hundreds of thousands of hours without degradation or catastrophic failure. The present invention is directed to providing laser devices and methods for their construction which can meet this growing demand.